444 C. Bar us and V. Strouhal — Strain-effect of sudden 



that the density-effect of the annealing of hard steel is out of 

 all proportion and symmetry with the strain effect and the 

 corresponding electrical effect. We were desirous therefore of 

 studying the temper-strain in substances other than steel and 

 free from carbon. Long ago, glass had suggested itself to 

 us for this purpose.* We communicate in the following Table 

 II the density effect produced by successive annealing of ordi- 

 nary Prince Eupert drops. Twelve of these were in hand. 

 Three were broken to test the strain, the remainder examined. 

 All the drops contained included bubbles, one or more, often 

 0'2 cm to O3 om in diameter and distributed irregular^. Usually 

 a few large bubbles predominated. The drops moreover 

 showed a purple coloration, which disappeared after annealing 

 at incipient redness. f To anneal the drops at different temper- 

 atures we enclosed them in a test-tube, cushioned upon and 

 surrounded by carded asbestos. The end of the tube was sub- 

 merged sufficiently to cover the P. E. drops in boiling camphor, 

 mercury, sulphur, etc., as given in the table. To anneal at red 

 heat, the drops were suspended in little baskets of platinum 

 foil, in the center of large thick clay crucible and then heated 

 to the desired temperature in an assay furnace. Under all 

 circumstances but one, care was taken to cool the drops slowly. 

 Table II contains under "temper" the temperature and time of 

 annealing, not including the time of cooling, however. The 

 column m gives the weight of each drop in grams. Variations 

 of m are due to accidental breakage of the frail stems of the 

 drops. Where no such breakage occurs m is constant. J 0) 

 finally, is the density of the drops at 0° C, under the conditions 

 given. Each J a is the mean of two independent determina- 

 tions and is warranted correct to within one or two units of the 

 third place. 



Table III following is constructed to facilitate a comparison 

 of the important data. The second and third columns contain 

 the densities of the extreme states of temper, the original 

 quenched, " hard," and the final " soft" or thoroughly annealed 

 state. The remaining columns contain the increments of density 

 due to quenching, relative to the density of the soft state, the 

 relative increments in other words which are retained at the 

 divers temperatures given. 



*Wied. Ann., vii, p. 406. 1879. 



f The color of the drops is amethystine ; the powdered glass pink. 



